Vehicle road simulation has been an effective development and validation tool within the ground-vehicle industry for many years. Full-vehicle road simulation facilities generally fall into two primary configurations: tire-coupled simulators, known as 4-Posters (FIG. 1), and spindle-coupled simulators (FIG. 2). As seen in FIG. 1, a 4-Poster tire-coupled simulator 10 has four posts 12 each with a platform 14 onto which a tire 16 of a vehicle 18 is attached. The 4-Poster has traditionally been used for body and body-component structural durability testing, evaluation of vehicle squeak and rattle characteristics, and performance testing of suspension control systems, as described in "Road Simulators in Car Body Structural Testing", F. Massaglia and E. Rossetto, Intl. Seminar on Techniques for Testing Vehicles and Related Structural Components, Torino Italy, 1984. Use of 4-Posters for suspension development and validation is limited, however, due to the lack of significant loading in the longitudinal, lateral, and brake moment axes.
A spindle-coupled simulator 20 (FIG. 2), on the other hand, can introduce from three to five forces and moments at each vehicle spindle 22. The tires of a vehicle 24 to be tested are removed and simulator controlled apparatus 26 is connected at each spindle 22. These simulators, although more expensive and complicated to operate, comprehensively test the complete vehicle for structural durability, except for internal powertrain components ("Three Years of Experience with the Audi Simulator", J. Petersen, Intl. Seminar on Techniques for Testing Vehicles and Related Structural Components, Torino Italy, 1984).
Industry-standard techniques for the control of road simulators, such as a spindle-coupled simulator, have been widely documented ("Road Simulation System for Heavy Duty Vehicles", Cryer et al., SAE Paper 760361, 1976). These techniques normally rely on the principle of "response simulation". In general, response simulation is an approach which uses experimentally determined models of simulator and vehicle dynamics to predict test control signals which force a desired vehicle response. These test control signals, which typically represent suspension component forces, accelerations, and wheel-to-body displacements, are determined from experimental responses gathered during a test run of an instrumented vehicle over a road, typically at a proving ground facility. As seen in FIG. 3A, a vehicle A having a certain configuration is driven over a road surface 32. Data is collected which can be reduced to a spindle force history 34, or the spindle force history 34 can be collected directly from the spindle. The procedure is shown in FIG. 4. In box 40, the vehicle is instrumented, driven over the road, and data is collected. In ellipse 42, vehicle dependent parameters, such as suspension component force or acceleration, are determined. These parameters are fed into a model of the simulator and vehicle dynamics in box 44 which produces a set of test control signals, referred to as a simulator "drive file" in ellipse 46. These test control signals are then capable of forcing the spindle-coupled simulator 48 to produce spindle-forces representative of those that were experienced when the vehicle was driven over the proving grounds road. The vehicle can then be further tested more efficiently on the spindle-coupled simulator.
For a vehicle having a different configuration, such as vehicle B in FIG. 3B, driven over the road surface 32, a different spindle force history 36 will be collected due to dynamics changes resulting from configuration differences between vehicles A and B. The process in FIG. 4 is therefore required to be run again and a separate simulator drive file developed for vehicle B to achieve further accurate testing. The vehicle instrumentation and data acquisition phase required to obtain the develop the simulator drive files for each vehicle can take from 6 to 8 weeks. Once the experimental responses have been gathered for a particular vehicle, further testing can be accomplished on a spindle-coupled road simulator through response simulation using the test control signals as input.
One alternative is to use the spindle force history of vehicle A as an input to vehicle B, as shown in FIG. 5. Essentially, the test control signals on the drive file for vehicle A would be used for testing vehicle B. The data acquisition phase for vehicle B would thus be eliminated (FIG. 6), thus reducing vehicle development time and cost. It has been found, however, that using the test control signals developed for one vehicle configuration does not provide a good approximation of actual road conditions for other vehicle configurations when attempting to simulate road conditions on a spindle-coupled simulator. This is so since vehicle configuration changes such as suspension level, suspension-to-body clearance, and vehicle ballast have a significant impact on the dynamics of the spindle, particularly due to the absence of tires in a spindle-coupled simulator.
Prior methods for mechanically re-introducing tire compliance into the spindle-coupled simulation process have been only partially successful. One such method, disclosed in U.S. Pat. No. 4,981,034 (Haeg), involved adding an adjustable gas-spring to a simulator vertical fixture, which could be tuned to approximate the dynamics of a physical tire. Another incorporated the vehicle tire into the simulator using a platform and strap restraint. Both of these solutions required expensive, major modifications to the simulation equipment, and had associated limitations. For example, the tire-spring emulator offered only vertical compensation, and the tire/strap configuration over-constrained the suspension in the vertical rebound direction. In addition to mechanical modification of the spindle-coupled simulator, modification of the simulator servo-hydraulic control system to simulate a tire has also been attempted. Initial attempts to incorporate a "tire" into the closed-loop controller using simple proportional-derivative force feedback failed to provide any significant dynamic tire compliance.
As a result of this lack of an acceptable method for emulating the tire dynamics for a spindle-coupled simulator, the traditional approach has been to record experimental responses for each vehicle configuration to be tested, install each such vehicle on the simulator, and re-develop test control signals that are specific for each vehicle configuration, as described above with respect to FIGS. 3A, 3B and 4. This approach significantly slows vehicle development due to the time required to instrument the vehicle and collect the data for each configuration, particularly for vehicles which have many combinations of structural attributes, such as body-styles, suspensions, and wheelbases. A process which provides "generic" test control signals For spindle-coupled simulators regardless of vehicle configuration is therefor needed to reduce vehicle development time.